Antibody-drug conjugates (ADCs) present unique challenges for analytical scientists. For small molecules, method development is generally fairly straightforward, while for biologics, platform methods are often available, removing the requirement for de novo validation. ADCs, however, sit in between these two modalities, combining them into a single modality. This duality makes every analytical development case a special case.
Take conjugation, for example. The way that the two components are connected fundamentally changes the analytical landscape. It might be via the random and unselective technique of lysine conjugation; it could be using cysteine conjugation, which is still random but has some regioselectivity; or perhaps a site-specific technique is used, offering far greater control. Each strategy will impact the nature of the conjugation, and therefore the method.
The drug-to-antibody ratio (DAR) will also vary. The number commonly lies between one and eight for both regioselective and site-specific conjugation, which also affects method development. And then there is the drug linker itself: is it hydrophobic, bulky charged? Every physicochemical property adds layers of complexity to method development.
Impact of novel modalities
The ADC field is moving beyond the standard drug linker molecules, conjugation strategies, and proteins. Regarding protein modalities, bispecific antibodies, VHH domain Fc fusions, Fab2/Fab-fragments, single-chain variable fragments and even VHH nanobodies instead of IgG scaffolds are now being investigated. Each new modality further stretches analytical strategies.
All this diversity of components and chemistries rules out the development of a platform approach. Although there are multiple standard methods that can provide useful starting points, each individual ADC will still require a specific method to be developed, optimised and validated.
These standard methods cover a significant number of specific modalities, and it is often possible to adapt them to make them more product-specific. Alternatively, they can provide a starting point for new method development. Either way, validation remains a must for each new product. This approach provides a faster and cheaper alternative to implementing a customer-developed method, which may use different analytical equipment and therefore require additional work, or developing a completely new method from scratch.
Lonza’s approach
At Lonza, we’ve built an analytical toolbox broad enough to meet these challenges. Over the past several years, we’ve expanded our set of standard methods to cover most critical quality attributes across a wide range of different modalities. Some methods, such as those covering DAR distribution, will likely require different strategies. The skill lies in determining whether, and how, the standard methods can be applied.
A great example is our Ibex® Design ADC Program, which integrates speed, quality, and efficiency to facilitate short timelines to IND. The methods included within the DNA-to-IND programme are key to achieving fast timelines and help mitigate development risks for cytotoxic bioconjugates.
Of course, the toolbox is not static. We continuously assess available standard methods and evaluate emerging technologies and new instrument platforms to refine accuracy, speed, and robustness. The breadth of knowledge across Lonza allows us to share best practices with our colleagues working on proteins and small molecules.
Ultimately, ADC analytics is definitely not a plug-and-play exercise; every method requires validation. But there is no substitute for experience, and that’s something Lonza has in abundance. Since 2006, Lonza has supported over 70 ADC programs from preclinical development to commercial-scale manufacturing. That track record means we know when to adapt, when to innovate, and how to keep timelines intact while upholding quality.